Method of manufacturing pin photodiode

ABSTRACT

The objective of this invention is to provide a type of photodiode and the method of manufacturing the photodiode characterized by the fact that it has a higher photoelectric conversion efficiency (sensitivity) than that in the prior art. PIN photodiode  100  has a p-type silicon substrate, p-type silicon layer  112,  n-type silicon layer  114  formed on p-type silicon layer  112  and having a junction plane with silicon layer  112,  n-type low-resistance silicon region  116  that is formed to a prescribed depth from the surface of silicon layer  114  and has an impurity concentration higher than that of silicon layer  114,  silicon oxide film  120  formed on silicon region  116,  and silicon nitride film 122 formed on silicon oxide film  120.

FIELD OF THE INVENTION

The present invention pertains to a type of photodiode used in anoptical pickup or other light receiving element. In particular, thepresent invention pertains to a type of PIN photodiode that can receivewavelengths of blue light with high sensitivity.

BACKGROUND OF THE INVENTION

The PIN photodiode is an element that has a P-I-N structure with anintrinsic layer (high resistance epitaxial layer or the like) between ap-type semiconductor and an n-type semiconductor, and that convertsincident light to a photocurrent. Its principle of operation is asfollows: when light with energy higher than the band-gap energy isincident on silicon (Si) having a PIN structure with a reverse biasapplied to it, electron-hole pairs are generated in the silicon crystal.As photocarriers, electrons move to the N layer, while holes move to theP layer, and a back current is output.

For example, Patent Reference 1 has disclosed a method of manufacturinga photodiode characterized by the following facts: as shown in FIG. 6(a), p-type semiconductor layer 12 is formed on the outer layer of n-typesemiconductor layer 11; mask layer 30 and insulating layer I are formedon p-type semiconductor layer 12; and, as shown in FIG. 6( b), with masklayer 30 being used as an etching stopper, opening H is formed ininsulating layer I; and mask layer 30 within opening H is removed bymeans of wet etching to form the photodiode. As a result, it is possibleto inhibit leakage caused by etching damage.

In addition, Patent Reference 1 has disclosed a type of photodiodecharacterized by the following facts: as shown in FIG. 7, plural p-typesemiconductor layers 12 are formed in a checkerboard configuration inn-type semiconductor layer 11, and antireflection film AR made ofsilicon oxide film 25 and silicon nitride film 26 is formed on thesilicon surface to create the photodiode.

[Patent Reference 1] Japanese Kokai Patent Application No. 2001-20079

Due to its properties, silicon can only convert light with wavelengthsin the range of 400-1100 nm into a photocurrent for output. This isbecause the photon energy of light with a wavelength longer than 1100 nmis lower than the band-gap energy (1.12 eV) of silicon, so that theelectron-hole pair cannot be formed. On the other hand, theshort-wavelength light can generate the electron-hole pair only near thesilicon surface. Because the silicon surface usually has a very highrecombination speed, the electron-hole pairs formed under light with awavelength shorter than 400 nm are immediately recombined, and thephotocarriers in the silicon are annihilated.

The PIN photodiode has two important characteristics, namely sensitivity(photoelectric conversion efficiency) and BW (response speed). FIG. 8 isa cross section illustrating a PIN photodiode with a constitution formedtaking into consideration said two important characteristics withrespect to the blue light wavelength (λ=405 nm) based on the fundamentalprinciple of the PIN photodiode. As shown in the figure, lowconcentration p-type silicon layer 41 is formed on high-concentrationp-type monocrystalline silicon substrate 40, and low concentrationn-type silicon layer 42 is formed by epitaxial growth on said p-typesilicon layer. When a reverse bias voltage is applied, a depletionregion is formed between said p-type silicon layer 41 and n-type siliconlayer 42, and when light is incident on it, electron-hole pairs aregenerated.

Intermediate concentration n-type silicon regions 43, 44 are formed inn-type silicon layer 42. Plural silicon regions 43 are arranged in agrid configuration on the light receiving plane. High concentrationn-type contact regions are formed in said silicon regions 43, 44,respectively, and contact regions are respectively connected to theplatinum silicide (PtSi) or other electrodes 45, 46.

High concentration p-type channel stop region 48 connected to p-typesilicon layer 41 is formed below field oxide film 47. Metal wiring 49 iselectrically connected via high concentration p-type contact region 50to p-type silicon layer 41, and metal wiring 51 is connected toelectrode 46. Electrode 45 within the light receiving plane iselectrically connected to metal wiring 51 at a position not shown in thefigure. Multilayer insulating layer 52 is formed on field oxide film 47.Opening H is formed in multilayer insulating layer 52 to define thelight receiving plane. The silicon surface exposed in opening H iscovered with silicon nitride film 53, and its upper surface is coveredwith silicon nitride protective film 54.

With a reverse bias voltage applied between metal wirings 49, 51, adepletion region is formed between p-type silicon layer 41 and n-typesilicon layer 42. Because n-type silicon layer 42 is much thinner thanp-type silicon layer 41, the depletion region reaches the siliconsurface. Electron-hole pairs are generated in the depletion region whenlight is incident on it. The holes flow from p-type silicon layer 41 tometal wiring 49, electrons flow to electrode 45 near the depletionregion, and the current obtained by photoelectric conversion is output.

Grid-like high concentration silicon regions 43 and electrodes 45 areplaced near the surface in the PIN photodiode so that the shortwavelength blue light can generate photocarriers near the surface ofsilicon. As a result, a low concentration layer is formed between thegrids, the depletion layer can spread effectively, and photocarriers canbe generated even at the blue light wavelength. Because said grid-likehigh concentration silicon regions 43 and electrodes 45 are arrangedadjacent to the depletion region where the photocarriers are generated,the generated photocarriers can move smoothly through high concentrationsilicon regions 43 toward electrodes 45 before being annihilated insilicon to form a photocurrent, and the photoelectric conversionefficiency is optimized with respect to the blue light wavelength. Here,the photoelectric conversion efficiency refers to the ratio of thecurrent obtained by photoelectric conversion to the power of theincident light.

The photoelectric conversion efficiency is as high as about 0.284 A/Wfor a PIN photodiode using the blue light wavelength with thisconstitution. However, the theoretical threshold is 0.327 A/W, which hasnot yet been reached. In order to achieve a value nearer to thetheoretical threshold, electrodes 45 should not be positioned within thelight receiving plane (opening H). Said electrodes 45 within the lightreceiving plane block the incident light, so that the number of carriersgenerated in the depletion region decreases and the photocurrenttherefore falls, contributing significantly to a decrease in thephotoelectric conversion efficiency. On the other hand, if there are noelectrodes 45 in the light receiving plane, the travel distance of thecarriers increases and the proportion of carriers annihilated due torecombination of the carriers near the silicon surface becomes higher,leading to a decrease in the photoelectric conversion efficiency. Thisis an antinomy topic.

The purpose of the present invention is to solve the aforementionedproblems of the prior art by providing a type of photodiode and a methodof manufacturing the photodiode having a higher photoelectric conversionefficiency (sensitivity) than that in the prior art.

In addition, a purpose of the present invention is to provide a type ofphotodiode and a method of manufacturing the photodiode with a highphotoelectric conversion efficiency for blue light or other shortwavelength light.

SUMMARY OF THE INVENTION

The present invention provides a method of manufacturing a photodiodecharacterized by the fact that it has the following processing steps: ona first silicon layer of the first electroconductive type, a secondsilicon layer of the second electroconductive type is formed; a siliconregion of the second electroconductive type and having an impurityconcentration higher than that of the second silicon layer is formed ata prescribed depth from the surface of the second silicon layer; asilicon oxide film is formed on the surface at least including saidsilicon region; and an antireflection film is formed to cover a portionor the entirety of said silicon oxide film.

As a preferred scheme, said silicon oxide film is formed by thermaloxidation; antireflection film is a silicon nitride film; the filmthickness of said silicon oxide film is about 50-120 Å and the filmthickness of the silicon nitride film is about 400-600 Å; and the filmthickness of the silicon nitride film depends on the wavelength of theblue light.

Also, the following scheme is preferred: the resistivity of said siliconregion is 0.02-2 Ω·cm, the resistivity of the second silicon layer is2-4 Ω·cm, the depth of said silicon region from the surface of thesecond silicon layer is about 0.5 Å, and the thickness of said secondsilicon layer is about double said depth; and said silicon region isformed by ion implantation of an impurity.

The following method of manufacturing a photodiode is preferred: themethod of manufacturing a photodiode also has a processing step offormation of an insulating film to cover said antireflection film, aprocessing step in which an opening is formed in said insulating film toexpose at least a portion of said antireflection film, and a processingstep in which first and second electrodes are formed to provideelectrical connection to said first silicon layer and said secondsilicon layer, respectively; said first and second electrodes arearranged on the outer side with respect to said opening.

The present invention provides a method of manufacturing a semiconductordevice characterized by the fact that the method of manufacturing thesemiconductor device containing a photodiode and MOS transistor has thefollowing processing steps: on a first silicon layer of the firstelectroconductive type, a second silicon layer of the secondelectroconductive type is formed; a silicon region of the secondelectroconductive type and having an impurity concentration higher thanthat of the second silicon layer is formed at a prescribed depth fromthe surface of the second silicon layer; when the gate oxide film ofsaid MOS transistor is formed, said gate oxide film is formed on thesurface of said silicon region; an antireflection film is formed tocover a portion or the entirety of said silicon oxide film of thephotodiode; and an opening is formed in the insulating film formed onthe antireflection film to expose at least a portion of theantireflection film.

The present invention provides a type of photodiode characterized by thefact that it has the following parts: a substrate, a first silicon layerof the first electroconductive type formed on the substrate, a secondsilicon layer of the second electroconductive type formed on said firstsilicon layer and including the junction plane with said first siliconlayer, a silicon region of the second electroconductive type formed at aprescribed depth from the surface of said second silicon layer andhaving an impurity concentration higher than that of the second siliconlayer, a silicon oxide film formed on said silicon region, anantireflection film formed on said silicon oxide film, and an insulatingfilm with an opening formed in it to expose at least a portion of saidantireflection film.

As a preferred scheme, the photodiode also has a first electrode and asecond electrode on the outer side with respect to said opening; thefirst electrode is electrically connected to the first silicon layer;and the second electrode is electrically connected to the second siliconlayer. The aforementioned photodiode includes an optical pickup or otherlight receiving device, and the light receiving device receives aportion of the light exiting from said light source or the lightreflected from said recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of the optical pickup usingthe PIN photodiode in the application example of the present invention.

FIG. 2 is a diagram illustrating an example of the circuit formed on thesilicon chip of the light receiving device shown in FIG. 1.

FIG. 3 is a cross section illustrating schematically the constitution ofthe PIN photodiode in the application example of the present invention.

FIG. 4A is a schematic cross section illustrating the process ofmanufacturing the PIN photodiode in the application example of thepresent invention.

FIG. 4B is a schematic cross section illustrating process ofmanufacturing the PIN photodiode in the application example of thepresent invention.

FIG. 4C is a schematic cross section illustrating the process ofmanufacturing the PIN photodiode in the application example of thepresent invention.

FIG. 4D is a schematic cross section illustrating the process ofmanufacturing the PIN photodiode in the application example of thepresent invention.

FIG. 5 is a diagram illustrating the characteristics of the PINphotodiode in this application example.

FIG. 6 is a cross section illustrating the constitution of a PINphotodiode in the prior art.

FIG. 7 is a cross section illustrating the constitution of a PINphotodiode in the prior art.

FIG. 8 is a cross section illustrating the constitution of a PINphotodiode in the prior art.

REFERENCE NUMERALS AND SYMBOLS AS SHOWN IN THE DRAWINGS

In the figures, 60 represents an optical pickup, 62 represents a lightsource, 64 represents a splitter, 66 and 68 represent a light receivingdevice, 70 represents a semiconductor silicon chip, 72 represents aperipheral circuit, 100 represents a PIN photodiode, 110 represents ap-type silicon substrate, 112 represents a low concentration p-typesilicon layer, 114 represents a low concentration n-type silicon layer,116 represents an intermediate concentration n-type silicon region, 118represents a field oxide film, 120 represents a silicon oxide film, 122represents a silicon nitride film, 124 represents a high concentrationn-type contact region, 126 represents a silicide layer, 128 represents aelectrode, 130 represents a high concentration p-type contact region,132 represents a silicide layer, 134 represents an electrode, 136represents a multilayer insulating film, 138 represents a protectivefilm, 150, 162 and 164 represent a resist mask, 152 represents anopening, 154 represents an ion implantation, 160 represents apolysilicon layer, H represents an opening.

DESCRIPTION OF THE EMBODIMENTS

Compared with the conventional photodiode, the photodiode of the presentinvention has a higher photoelectric conversion efficiency without adecrease in the response speed for the blue light wavelength. Inaddition, by using the photodiode of the present invention in an opticalpickup, it is possible to read data from a recording medium or writedata with high precision.

In the following, the optimum embodiment of the present invention willbe explained in more detail with reference to figures. This explanationwill be made with respect to an example of a PIN photodiode for use asthe light receiving element of an optical pickup having a blue lightsource for reading data from a DVD or other recording medium or forwriting data.

FIG. 1 is a diagram illustrating an example of the constitution of theoptical pickup. Here, optical pickup 60 performs optical reading of thedata recorded on a disk driven to rotate, or optical writing of thedata. Said optical pickup 60 has light source 62 containing a bluelight-emitting laser element or laser diode, splitter 64, and lightreceiving devices 66, 68. Said splitter 64 reflects the blue lightemitted from light source 62 onto disk D, and at the same time lets aportion of the light pass through it to go to light receiving device 66.In addition, the light reflected from disk D also passes through ittoward light receiving device 68. Said light receiving device 66monitors the light output from light source 62, and stabilizes theoptical output of blue light based on the monitoring result. Said lightreceiving device 68 monitors the light reflected from disk D, andperforms focusing and tracking control based on the result. Lightreceiving device 68 also is used in reading the data written on disk D.

Each of light receiving devices 66, 68 contains a PIN photodiode forreceiving the blue light. Said light receiving devices 66, 68 can eachcontain a peripheral circuit for amplifying or processing the signaldetected by the PIN photodiode. For example, as shown in FIG. 2, PINphotodiode 100 and its peripheral circuit 72 can be integrated in asingle semiconductor-silicon chip 70. Here, peripheral circuit 72 is anintegrated circuit containing plural MOS transistors, etc.

FIG. 3 is a cross section illustrating the structure of the PINphotodiode in an application example of the present invention. In PINphotodiode 100 of this application example, low concentration p-typesilicon layer 112 formed by means of epitaxial growth, low concentrationn-type silicon layer 114 formed by epitaxial growth, and intermediateconcentration n-type silicon region 116 having a prescribed depth fromthe surface of silicon layer 114 are formed on high concentration p-typemonocrystalline silicon substrate 110. When a reverse bias voltage isapplied, the depletion region spreads up/down from the junction planebetween silicon layer 112 and silicon layer 114.

Said silicon region 116 is defined by field oxide film 118. Thermaloxidation of silicon region 116 is performed to form silicon oxide film120, and silicon nitride film 122 is formed on silicon oxide film 120.Said silicon oxide film 120 and silicon nitride film 122 form anantireflection film.

High concentration n-type contact region 124 is formed on each of thetwo end portions of n-type silicon region 116. Said contact region 124is electrically connected via platinum silicide (PtSi) layer 126 toelectrode 128. It also extends via n-type silicon layer 114 to p-typesilicon layer 112 to form high concentration p-type contact region 130.Said contact region 130 is electrically connected via platinum silicide(PtSi) layer 132 to electrode 134.

In addition, multilayer insulating film 136 and protective film 138 areformed on the silicon substrate. Opening H is formed in said multilayerinsulating film 136 and protective film 138 to expose silicon nitridefilm 122. Said opening H defines the light receiving plane of the PINphotodiode. When a reverse bias voltage is applied to electrode 128 onthe cathode side and electrode 134 on the anode side, a depletion regionis formed from the interface between silicon layer 112 and silicon layer114. The depletion region almost reaches the silicon surface region, andwhen blue light is incident on opening H, electron-hole pair carriersare formed in the depletion region. The electrons move to electrode 128on the cathode side, and the holes move to electrode 134 on the anodeside and a photocurrent is output as a result.

In this application example, PIN photodiode 100 is different from theconventional photodiode shown in FIG. 8 in which grid-like electrodesare arranged on the light receiving plane. As explained above, in theprior art the electrodes in the light receiving plane block a portion ofthe incident light L, leading to a decrease in the quantity of incidentlight in the depletion region, and thus causing a decrease in thephotoelectric conversion efficiency (sensitivity). On the other hand,the PIN photodiode of the present invention has essentially noelectrodes blocking incident light L on the light receiving plane.Consequently, unlike in the conventional PIN photodiode havingelectrodes arranged there, it is possible to prevent a reduction in thequantity of incident light in the depletion region.

On the other hand, when electrodes are not arranged on the lightreceiving plane, the travel distance of the carriers generated in thedepletion region near the silicon surface becomes greater, and theannihilation proportion due to recombination becomes higher. Inparticular, when there are plural silicon free bonds (dangling bonds) onthe silicon surface, the carriers are trapped in the trap level of thesilicon interface, and the probability of annihilation of the carriersdue to recombination becomes higher. In this application example,because silicon oxide film 120 is formed by thermal oxidation on siliconregion 116, the number of dangling bonds of silicon decreases, so thatthe interface state becomes stable, and the interface trappingphenomenon can be minimized. Also, silicon oxide film 120 is highlyreflective of light, but by forming silicon nitride film 122 directlyabove silicon oxide film 120 it is possible to prevent the reflection ofblue light L. Said silicon nitride film 122 is formed with anappropriate film thickness with respect to the blue light, withoutrestriction by design or operating process.

In addition, when the resistance of the silicon surface becomes high,the carrier movement velocity becomes lower, and the response speedfalls. In order to avoid this problem in this application example, highconcentration n-type silicon region 116 is formed to a prescribed depthfrom the surface of n-type silicon layer 114. It is preferred thatsilicon region 116 have a depth of about 0.5 μm from the siliconsurface. Taking into consideration the properties of silicon it ispreferred that a depletion region be formed on the silicon surface toensure that the blue light wavelength is absorbed by the siliconsurface. Consequently, in order to ensure that high concentrationsilicon region 116 does not become a hindrance to formation of thedepletion region, silicon region 116 is formed within a prescribed depthfrom the silicon surface. As a result, the carriers generated near thesilicon surface move to silicon region 116 near the silicon surface witha low resistance, and it is possible to inhibit a decrease in theresponse speed.

In the following, the manufacturing process of the PIN photodiode inthis application example will be explained with reference to FIGS.4A-4D. Here, as an example, the case will be explained in which the PINphotodiode and the MOS transistors of the peripheral circuit are formedon a semiconductor chip. As shown in FIG. 4A, first of all, highconcentration p-type monocrystalline silicon substrate 110 is prepared.For example, silicon substrate 110 has a thickness of 610-640 μm and aresistivity (specific resistance) in the range of 0.01-0.02 Ω·cm. Forexample, boron is used as the impurity.

Low concentration p-type silicon layer 112 is formed by means ofepitaxial growth on silicone substrate 110. For example, silicon layer112 has a thickness of 25 μm and a resistivity of 1000-4000 Ω·cm. Inaddition, low concentration n-type silicon layer 114 is formed by meansof epitaxial growth on silicon layer 112. For example, silicon layer 114has a thickness of about 0.9 μm and a resistivity in the range of 2-4Ω·cm. Also, high concentration p-type contact region 130 is formed at adepth from field oxide film 118 to reach p-type silicon layer 112. Saidcontact region 130 is formed by means of ion implantation of B (boron).

Resist mask 150 is formed on the silicon substrate formed with saidconstitution. Opening 152 is formed in resist mask 150 to expose siliconlayer 114 defined by field oxide film 118. Thermal oxidation isperformed on the surface of said exposed silicon layer 114 to form asilicon oxide film with thickness of about 300 Å for ion implantation.Then, ion implantation of P (phosphorus) or As (arsenic) is performedover the entire surface of the substrate via the silicon oxide film forion implantation, and n-type silicon region 116 with an intermediateconcentration is formed in silicon layer 114 left exposed by resist mask150. Said silicon region 116 is formed with a depth of about 0.5 μm fromthe silicon surface, and has a resistivity of 0.02-2 Ω·cm.

After removal of the silicon oxide film for ion implantation and resistmask 150, as shown in FIG. 4B, silicon oxide film 120 is formed onsilicon region 116. As explained above, when the MOS transistors of theperipheral circuit are formed on the silicon chip, the gate oxide filmmay be used as silicon oxide film 120. It is preferred that siliconoxide film 120 be formed by means of thermal oxidation performed suchthat the silicon substrate is exposed to a temperature in a prescribedrange. It is preferred that silicon oxide film 120 be formed with athickness of about 50-120 Å. Formation of silicon oxide film 120 causesthe dangling bonds on the surface of the silicon to be bonded withoxygen, and the number of dangling bonds is reduced.

Polysilicon layer 160 is then formed on silicon oxide film 120. Saidpolysilicon layer 160 is used in the gate of the MOS transistor. Saidpolysilicon layer 160 has a thickness of about 3000-3750 Å. Resist mask162 is formed on polysilicon layer 160 by means of a well-knownphotolithographic process, and polysilicon layer 160 is patterned viaresist mask 162. Said polysilicon layer 160 protects silicon oxide film120 until immediately proceeding the formation of silicon nitride film122 on silicon oxide film 120.

After the removal of resist mask 162, high concentration contact region130 is formed on p-type silicon layer 112, and high concentrationcontact region 124 is formed in silicon region 116. As shown in FIG. 4C,resist mask 164 is formed on the silicon substrate, and polysiliconlayer 160 is etched away via resist mask 164. As a result, silicon oxidefilm 120 is exposed. After the removal of resist mask 164, siliconnitride film 122 is formed as shown in FIG. 4D. It is preferred thatsilicon nitride film 122 be formed by means of reduced pressure CVD.When silicon oxide film 120 has the aforementioned film thickness, thefilm thickness of silicon nitride film 122 is preferably in the range of400-600 Å. The film thickness of silicon oxide film 120 and siliconnitride film 122 is selected so that reflection of the blue lightwavelength is minimized.

FIG. 5 is a diagram illustrating the results of measurement of thecharacteristics (measurement results) of the PIN photodiode with saidconstitution. The incident light has a wavelength of 405 nm, and thereverse bias voltage applied to the PIN photodiode is 2.0 V. As can beseen from the figure, the photoelectric conversion efficiency of the PINphotodiode in the prior art (structure shown in FIG. 8) is 0.284 A/W,and the photoelectric conversion rate of the PIN photodiode in thisapplication example is 0.319 A/W. The value has been increased to nearthe theoretical threshold. In addition, while the bandwidth of the PINphotodiode of the prior art is 240 MHz, the bandwidth of the presentapplication example is 334 MHz, and the response speed is alsoincreased.

The above detailed explanation has provided for on the preferredembodiment of the present invention. However, the present invention isnot limited to the prescribed embodiment. Various modifications can bemade as long as the gist described in the claims is observed.

In the aforementioned application example, an explanation has beenprovided for the manufacturing method when PIN photodiode and MOStransistors as peripheral circuit are contained in the silicon chip. Ofcourse, the present invention may also be applied to the method ofmanufacturing individual PIN photodiode transistors without MOStransistors. In addition silicon nitride film is used as theantireflection film in said application example. However, otherdielectric films or their combination may also be adopted as theantireflection film. Furthermore, the structure of the antireflectionfilm is not limited to two layers. More layers may also be adopted forthe multilayer structure. In said application example, the silicon layeris formed on the silicon substrate by means of epitaxial growth.However, formation of it is not limited to epitaxial growth.

1. A method of manufacturing a photodiode comprising the followingsteps: on a first silicon layer of the first electroconductive type, asecond silicon layer of the second electroconductive type is formed; asilicon region of the second electroconductive type and having animpurity concentration higher than that of the second silicon layer isformed at a prescribed depth from the surface of the second siliconlayer; a silicon oxide film is formed on the surface at least includingsaid silicon region; and an antireflection film is formed to cover aportion or the entirety of said silicon oxide film.
 2. The method ofmanufacturing a photodiode described in claim 1, wherein said siliconoxide film is formed by thermal oxidation.
 3. The method ofmanufacturing a photodiode described in claim 1 wherein saidantireflection film is a silicon nitride film.
 4. The method ofmanufacturing a photodiode described in claim 3, wherein the filmthickness of said silicon oxide film is about 50-120 Å, and the filmthickness of the silicon nitride film is about 400-600 Å.
 5. The methodof manufacturing a photodiode described in claim 4, wherein the filmthickness of the silicon nitride film depends on the wavelength of theblue light.
 6. The method of manufacturing a photodiode described inclaim 1, wherein: the resistivity of said silicon region is 0.02-2 Ω·cm,the resistivity of the second silicon layer is 2-4 Ω·cm, the depth ofsaid silicon region from the surface of the second silicon layer isabout 0.5 Å, and the thickness of said second silicon layer is aboutdouble said depth.
 7. The method of manufacturing a photodiode describedin claim 1 wherein said silicon region is formed by ion implantation ofan impurity.
 8. The method of manufacturing a photodiode described inclaim 1, wherein the first silicon layer is p-type, and the secondsilicon layer is n-type.
 9. The method of manufacturing a photodiodedescribed in claim 1, wherein the method of manufacturing a photodiodealso has a processing step of formation of an insulating film to coversaid antireflection film, a processing step in which an opening isformed in said insulating film to expose at least a portion of saidantireflection film, and a processing step in which first and secondelectrodes are formed to provide electrical connection to said firstsilicon layer and said second silicon layer, respectively; said firstand second electrodes arranged toward the outside of said opening.
 10. Amethod of manufacturing a semiconductor device having a photodiode andMOS transistor comprising the following steps: on a first silicon layerof the first electroconductive type, a second silicon layer of thesecond electroconductive type is formed; a silicon region of the secondelectroconductive type and having an impurity concentration higher thanthat of the second silicon layer is formed; at a prescribed depth fromthe surface 6 f the second silicon layer; when the gate oxide film ofsaid MOS transistor is formed, said gate oxide film is formed on thesurface of said silicon region; an antireflection film is formed tocover a portion or the entirety of said silicon oxide film of thephotodiode; and an opening is formed in the insulating film formed onthe antireflection film to expose at least a portion of theantireflection film.
 11. The method of manufacturing a semiconductordevice described in claim 10, further comprising a processing step inwhich when the polysilicon gate film of said MOS transistor is formed,said polysilicon gate film is formed on said gate oxide film, and saidantireflection film is formed after the removal of said polysilicon gatefilm.
 12. The method of manufacturing a semiconductor device describedin claim 11, wherein the film thickness of said gate oxide film is about50-120 Å, and said antireflection film is a silicon nitride film with afilm thickness of about 400-600 Å.
 13. The method of manufacturing asemiconductor device described in claim 11, wherein the resistivity ofsaid silicon region is 0.02-2 Ω·cm, and its depth from the surface ofthe second silicon layer is about 0.5 μm.
 14. A type of photodiodecomprising the following parts: a substrate, a first silicon layer ofthe first electroconductive type formed on the substrate, a secondsilicon layer of the second electroconductive type formed on said firstsilicon layer and including the junction plane with said first siliconlayer, a silicon region of the second electroconductive type formed at aprescribed depth from the surface of said second silicon layer andhaving an impurity concentration higher than that of the second siliconlayer, a silicon oxide film formed on said silicon region, anantireflection film formed on said silicon oxide film, and an insulatingfilm with an opening formed in it to expose at least a portion of saidantireflection film.
 15. The photodiode described in claim 14, wherein:the photodiode also has a first electrode and a second electrode on theouter side with respect to said opening; the first electrode iselectrically connected to the first silicon layer; and the secondelectrode is electrically connected to the second silicon layer.
 16. Thephotodiode described in claim 14, wherein the film thickness of saidsilicon oxide film is about 50-120 Å, and said antireflection film is asilicon nitride film with a thickness of about 400-600 Å.
 17. Thephotodiode described in claim 16, wherein the film thickness of thesilicon nitride film is determined according to the wavelength of theblue light.
 18. A type of light receiving device including thephotodiode described in claim
 14. 19. A type of optical readercharacterized by the fact that it includes the light receiving devicedescribed in claim 18, and a light source that irradiates a recordingmedium with blue light, and the light receiving device receives aportion of the light exiting from said light source or the lightreflected from said recording medium.